Some conventional positive crankcase ventilation (PCV) systems do not separate the oil from the gas that is in the engine blowby contained in the engine crankcase before recirculating it back into the air intake system of the engine. The blowby gas in the crankcase generally is mixed together in a gas/oil mixture. It is preferable to separate the oil from the engine blowby gas before feeding the blowby gas into the air intake system. It is desirable to aspirate the oil from the blowby gas in order to improve the oil economy of the engine by returning the separated oil to a sump to be re-used, and to reduce exhaust emissions by reducing the amount of oil that is circulated to the air intake system.
Automotive engine designers have used a variety of schemes to handle the flow of blowby gas originating in the crankcase and to separate the oil therefrom. Some of these systems employ centrifugal forces to separate the oil from the blowby gas. For those centrifugal types of oil separators already in the art, it is necessary to have a sealing type of mechanism between the rotating member and the structure that it is mounted to so that blowby gas that has not been through the centrifugal separator portion will not get into the clean gas that is flowing into the air induction system. This creates a concern with the wear and tolerances on typical seals, adding to the expense and complexity of the oil separator system.
Also, some oil separator systems rely solely on the vacuum pressure in the air induction system to operate, and may have difficulty operating optimally when vacuum pressure is low (i.e., at wide open throttle conditions). Further, an oil separator should be as compact as possible, to meet engine packaging requirements, and should require minimal power input from the engine to power it, while working adequately for all engine operating conditions.